1. Field of the Invention
The present invention is broadly concerned with novel, silicone compositions having long pot lives and that can be formed into high refractive index (“RI”) layers. The compositions are useful for forming solid-state devices such as flat panel displays, optical sensors, integrated optical circuits, light-emitting diodes (LEDs), microlens arrays, and optical storage disks.
2. Description of the Prior Art
A high RI value is highly desired to minimize internal reflection between compound semiconductor materials and the encapsulant materials used in high-brightness light-emitting diodes (HB LEDs). Historically, the development of materials with high refractive indices (RIs) started with the use of sputtering to deposit inorganic anti-reflective coatings on optical lenses, which is a high-cost, low-throughput process. Sol-gel coating technologies were developed to replace sputtering to produce inorganic films on the devices. However, sol-gel technologies involve a complicated manufacturing process, and they have many problems with storage stability and reliability. The optoelectronics industry is seeking more robust high RI materials that can be applied using existing equipment to achieve production at low cost and high throughput.
Various efforts to develop high RI materials have been undertaken, some involving the incorporation of heavy elements, such as bromine, or highly aromatic structures to increase RI.
Organic-inorganic hybrid coatings have also been developed. However, these coatings undergo more than 60% shrinkage during the curing process, which leads to high film stress and susceptibility to cracking for thicker films (>0.5 μm thick). The need for curing at temperatures higher than 200° C. is also a limitation for some device applications.
In addition, vacuum-deposited and chemical-vapor-deposited (CVD) optical coatings have been utilized in optoelectronics applications for many years. These coatings are traditionally limited to thin-film applications and are expensive to apply.
Finally, prior art compositions (particularly silicone-containing compositions) have short pot lives. That is, the ingredients must be provided in a two-part system because they begin to react upon mixing, and gelling occurs shortly thereafter, making the composition unusable. As a result, the end user must obtain the composition in two separate containers and mix the composition at the point and time of use. The composition must be used right away, before it becomes unusable. This results in the need to carry extra inventory, as well as to carry out additional steps during manufacturing, creating the potential for extra issues to arise with those steps.